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UIT2201: CS & the IT Revolution
Tutorial Set 9 (Spring 2008)

(D-Problems discussed on Thursday, 27-Mar-2008)
(Q-Problems due on Tuesday, 1-Apr-2008)
[Networking]

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Discussion Problems: -- Prepare (individually) for tutorial discussion.

T9-D1: (Transmitting images) Practice Prob 2 of Section 7.2.1 of [SG3].
Assume an uncompressed 1,200 x 780 image, with each pixel stored using an 8-bit gray scale representation that we want to transmit in under 1 second.
(a) What is the minimum acceptable transmission speed?
(b) What if the image is full color (RGB)?
(c) What about sending a 3-minute song in uncompressed MP3 format in under 1 second?

T9-D2: (Moving a Library, digitally) Prob 4 of Chap. 7 of [SG3].
(a) Assume there are 1 million books in your campus library. Approximate (to the nearest order of magnitude) how many bytes of data there would be if all these books were stored online and were accessible across a computer network.
(b) How long would it take to transfer the entire collection of books if the data rate of the transmission medium is 10 Mbps, the speed of the original Ethernet? How long would it take if we had a line with a speed of 1 Gbps? (This value represents the time needed to download your entire campus library!)
(Note: You can assume that an average book is represented by about 4 million bits (See Setion 4.2.2 of [SG3]).

T9-D3: (Ethernet Contention-based Protocol)
(a) Read up on the contention-based transmission technique used in the Ethernet protocol for Local Area Network LAN. This is covered in Sect 7.3.2 of [SG3].
(b) Then do Prob 5 on Ch.7 of [SG3].
Why is the address field needed in an Ethernet LAN protocol? Can you think of a useful situation where you might want either to omit the address field entirely or to use some "special" address value in the address field.

T9-D4: [Wide Area Network (WAN)]
(a) Read up on the Wide Area Networks (Sect. 7.2.3 of [SG3]) and Network Layer (Sect. 7.3.3 of [SG3].
(b) Then do Problem 13 of Chapter 7 of [SG3]

T9-D5: (URLs)
(a) Identify the components of the following hypothetical URL and describe the meaning of each.
      http://frogs.animals.com/animals/moviestar/kermit.html
(b) What about the following real URLs?
      http://www.didyouknow.cd/animals/frogs.htm
      http://www.comp.nus.edu.sg/~leonghw/uit2201/Sp2008/test.txt
      http://www.comp.nus.edu.sg/~leonghw/uit2201/Sp2008/Webpages/sample-webpage.html

T9-Q1: (5 points) [Transmitting images]
Prob 3 of Chapter 7 of [SG3].
Determine the total time it would take to transmit an uncompressed grayscale image (with 8 bits/pixel) from a screen resolution of 1,280 x 840 pixels using each of the following media: (i) A 56 Kbps modem (home phone dialup), (ii) A 2 Mbps DSL line (such as SingNet or Starhub), (iii) A 10 Mbps Ethernet link (Office LAN cable) or (iii) A 100 Mbps Fast Ethernet link (Office LAN cable)?

T9-Q2: (5 points) [LAN] Problem 6 of Chap. 7 of [SG3].
After reviewing the description of the Ethernet protocol in Section 7.3.2, how do you think this protocol would behave in a very heavily loaded network -- this is, a network environment where there are lots of nodes attempting to send messages? Explain what behaviour you would expect to see and why.

T9-Q3: (15 points) [WAN] (from past Quiz)
Given the following diagram, where the numbers next to each link represent the time delays across a link:

(a) List all the simple paths (those that do not repeat any node) from node C to node R. For each path, list the associated delay.
(b) What is the shortest path (with minimum delay) from node A to node F.
(c) Is the network shown above tolerant to single link failure? If not, give a simple way to make it so.
(d) Is the network shown above tolerant to single node failure? If not, give a simple way to make it so.

Definition:

• A network is said to be tolerant to single link failure if the network is still connected (every node in the network is able to talk to every other node) after a single link failure (no matter whick link fails).
• A network is said to be tolerant to single node failure if the network is still connected (every node in the network is able to talk to every other node) after a single node failure (no matter whick node fails).

A10: [Fault Tolerant Networks]
The issue of designing fault tolerant networks -- one that is tolerant to k link failures or to k node failures -- is an important area of research in network design. Discuss how you would accurately model and formulate these problems and describe some current research results in this area. (Use the web to search for relevant research articles.)